How does Google Suggest work? How does it manage to update the web page on the client so quickly, based on information in a distant Google database? Why does the web page not look ‘jumpy’ if it is being frequently updated?
It uses AJAX.
When you are writing your query, it searches for the 10 most requested words matching yours. Then it writes minified JSON on an invisible DIV element. Fast, but still resource intensive.
Try to install Firebug on Firefox or use the Developer Console on Chrome, open the console and start writing "Youtube" or whatever you want. You will see the minified JSON responses.
Good luck :D
In addition to the front-end handling others have talked about, which jQuery is a great example of, you might also be interested in how they approach the idea on the backend. Dr. Peter Norvig has written about how to create a spelling corrector, where similar approaches could be used to find close matches.
The whole page is not being updated. Only parts of it are using AJAX - Asynchronous Javascript and XML. Ajax requests can be made in Javascript, and the page updated when the response comes back.
A far more interesting question is how does Google actually search 10bn+ documents in a teeny tiny fraction of a second :)
How does Facebook Ajax work? 2-3 months ago they were using # but now the whole addressbar is changing.
The first approach used is called "Ajax Crawling" (also refer to this answer).
But I think the new approach you are talking about is just the HTML5 History API. Github is using this approach for their tree browsing, and you can learn more about it here. (I recommend ALL readers to read and watch the video as it's very informative)
EDIT:
Just to point out that Facebook is definitely using the HTML5 History API (direct link from the previous github article).
They still use # as far as I can tell (but maybe we are on different versions?). For me, their links are for different pages, but they intercept my onclick and change the click to an Ajax request instead. Maybe this is to make cleaner URLs when copying and/or make it work without JS?
I have to start using AJAX in a project and I don't know where to start. Can someone please help?
Asynchronous JavaScript And Xml. A technique for achieving bi-directional, script-driven communications between Web browsers and servers via HTTP.
See also:
definition on Wikipedia
AJAX Introduction on w3schools
Ajax Workshop 1 on Ajax Lessons
Edit: As pointed out by Nosredna, JSON is often used in place of XML.
The rough idea in English:
You have a web page. Some event (can be a button press or other form event, or just something triggered by a timer) occurs and triggers JavaScript code that asks the server for fresh information (like the latest value of GOOG stock).
There's a piece of code on the server that collects the info you passed and sends some info back. That's different from the page-serving job the server usually has.
When the server answers, a callback function (that you specified in the JavaScript call to the server) is called with the info from the server. Your JavaScript code uses the info to update something--like a GOOG stock chart.
Not to be confused with the cleaner, AJAX, the technology term, is really describing a framework or better stated as a technique for using XML and JavaScript to make asynchronous calls to server side code...
Here are some good code samples. And some more.
While many of these samples above show how to create all of the XML Request objects, if you look into the AJAX Control Toolkit from Microsoft for ASP.NET applications or jQuery, you'll find these easier to work with.
jQuery Sample (from jQuery site):
when code is hit, the some.php file is hit passing the name and location values in.
<script type="javascript">
function saveDataAjax(){
$.ajax({
type: "POST",
url: "some.php",
data: "name=John&location=Boston",
success: function(msg){
alert( "Data Saved: " + msg );
}
});
}
</script>
<input type="submit" onClick="saveDataAjax();" value="submit" />
It's a buzzword, the essence of it is:
Using Javascript to make an asynchronous HTTP request (in the background).
When the content arrives, an action is taken, usually performing some logic then updating the appearance of the page by manipulating the DOM tree; meaning, inserting new HTML elements, deleting some html elements, etc.
The X in AJAX stands for XML, but it's irrelevant. XML is just one of many ways to format the data that's sent by the server. JSON is a much better alternative (IMNSHO). Also, the server can send plain text or just regular html.
The keyword here is asynchronous request. A request that happens in the background, without the browser having to reload the page.
From the Pragmatic Ajax book:
What Is Ajax?
Ajax is a hard beast to distill into a
one-liner. The reason it is so hard is
because it has two sides to it:
Ajax can be viewed as a set of
technologies.
Ajax can be viewed
as an architecture.
Ajax: Asynchronous JavaScript and
XML
The name Ajax came from the bundling
of its enabling technologies: an
asynchronous communication channel
between the browser and server,
JavaScript, and XML. When it was
defined, it was envisioned as the
following:
Standards-based presentation using XHTML and CSS
Dynamic display and interaction using the browser’s DocumentObject
Model (DOM)
Data interchange and manipulation using XML and XSLT
Asynchronous data retrieval using XMLHttpRequest or XMLHTTP (from
Microsoft)
JavaScript binding everything together
Although it is common to develop using
these enabling technologies, it can
quickly become more trouble than
reward.
It is for these reasons that the more
important definition for Ajax is...
Ajax: The Architecture
The exciting evolution that is Ajax is
in how you architect web applications.
Let’s look first at the conventional
web architecture:
Define a page for every event in the application: view items, purchase
items, check out, and so on.
Each event, or action, returns a full page back to the browser.
That page is rendered to the user.
This seems natural to us now. It made
sense at the beginning of the Web, as
the Web wasn’t really about
applications. The Web started off as
more of a document repository; it was
a world in which you could simply link
between documents in an ad hoc way. It
was about document and data sharing,
not interactivity in any meaningful
sense.
Picture a rich desktop application for
a moment. Imagine what you would think
if, on every click, all of the
components on the application screen
redrew from scratch. Seems a little
nuts, doesn’t it? On the Web, that was
the world we inhabited until Ajax came
along.
Ajax is a new architecture. The
important parts of this architecture
are:
Small server-side events: Now components in a web application can
make small requests back to a server,
get some information, and tweak the
page that is viewed by changing the
DOM. No full page refresh.
Asynchronous: Requests posted back to the server don’t cause the
browser to block. The user can
continue to use other parts of the
application, and the UI can be updated
to alert the user that a request is
taking place.
onAnything: We can interact with the server based on almost anything
the user does. Modern browsers trap
most of the same user events as the
operating system: mouseovers, mouse
clicks, keypresses, etc. Any user
event can cause an asynchronous
request.
This all sounds great, doesn’t it?
With this change we have to be
careful, though. One of the greatest
things about the Web is that anybody
can use it. Having simple semantics
helps that happen. If we go overboard,
we might begin surprising the users
with new UI abstractions. This is a
common complaint with Flash UIs, where
users are confronted with new symbols,
metaphors, and required actions to
achieve useful results.
Most commonly, it refers to the use of the XMLHttpRequest object via JavaScript* in a browser.
Depending on who you ask, it could be used to describe almost any type of client/server communication over HTTP other than just typing a URL into a browser.
*jQuery provides some nice wrapper code to handle cross-browser differences, etc.
Ajax is a bit of a misnomer. To quote the wiki article:
Despite the name, the use of
JavaScript and XML is not actually
required, nor do the requests need to
be asynchronous.
Whereas now most people call "ajax" any type of
web application that communicates
with a server in the background
http://www.w3schools.com/Ajax/Default.Asp
that is a good place to start. This should answer all of your questions.
From the man that coined the term - http://adaptivepath.com/ideas/essays/archives/000385.php
"Ajax" is the successfull marketing term introduced back in 2005 to replace the the older term "DHTML" that did not stick well. "Ajax" today is part of the history too as the new word - "HTML5" emerge. Still "HTML5" is pretty much what original "DHTML" used to be.
Ajax is also reffered to as "the new approach to the application development" where a web page is created on the server initially but later on, during its lifetime, the updates are being done on the client as the data or partial content gets communicated to the server in a background.
Hope this clarifies.
Just to add.. may be not relevant for the question ..
although, AJAX was made famous by Gmail in their browser emails ..the credit of AJAX goes to Microsoft .. they created the AJAX thing..
I believe the fastest and easiest way to get started is with jQuery:
http://jquery.com/
http://docs.jquery.com/Ajax/jQuery.ajax#examples
AJAX stands for asynchronous JavaScript and XML, though it doesn't always deal with XML data anymore. Essentially it boils down to using the XMLHttpRequest object through JavaScript running on the client to make a web request and retrieve some information that you use to update the state of your page without requiring a page refresh.
Start with a basic tutorial that shows you how to use bare bones Ajax to make asynchronous requests such as http://www.w3schools.com/Ajax/Default.asp before moving on to using it in a production level application.
When using it in an application you're far better off investigating one of the common JavaScript frameworks that abstract away the differences between the various browsers and make it easy to manipulate the page after the request returns. I personally recommend http://www.jquery.com/
I read Head First AJAX as my first AJAX reference and I found it to give a simple and practical overview of AJAX.
Creative use of previously known technology. Both the browser side scripting and programmatic access to data on the server have been known before. In AJAX it has been put together for innovative use anabling new applications of thechology known before. The REST comes to mind as similar type of advance...
AJAX is very simple : someone somewhere tought that it would be cool to be able to send something to the server and receive something from it without reload a page.
AJAX is not a revolution, it's just a name for something simple : a web page can send a request to the server without being reloader - just some asynch stuff here.
You can add AJAX controls on your web pages wihout any works - just drag them in with Visual Studio. You may have to add some manager for them, but it is simply a drag-and-drop task.
But be warned : rogue web browser usually don't speak the same AJAX language as IE...
:)
AJAX is really fancy term for giving the browser the ability to refresh parts of its content with the need to reload an entire page. Like many have said, it doesn't require XML, or even Javascript in order to implement it. In fact in its early days it was done with with VBScript and Jscript and just called DHTML. Jesse James Garrett may have invented the AJAX term, but it was really Microsoft that invented the concept behind it.
This source says Microsoft started it in 1999, but I would date the birth of this technology even further. This Wired article is probably more accurate on the date of this technology being in the late 90's, much of it coming from the old days of the MSDN DHTML Dude columns written by Michael Wallent at Microsoft which started back in 1997. Much of the story is also told in this great video here by Michael himself: http://channel9.msdn.com/posts/Charles/Michael-Wallent-Advent-and-Evolution-of-WPF/ Megan still works at Microsoft by the way working on the Silverlight team nowadays, Microsoft's replacement for ActiveX.
Back to the AJAX thingy...when Jesse James Garrett back in 2005 he was mostly talking about the use of XMLHTTPRequest within Javascript code, and a dash of salt. That later began a hip word that many people started using even though they had no idea what it was, and thought that is really something brand new and hip, when really it was just a remix of something old.....sort of like many hip-hop songs you hear nowadays.
It's not new, just a newer version of something old!
I'll give it a try and say that "it's the concept of having a W3C based (JavaScript, HTML and CSS) solution for building Rich Applications for running on the web in a browser"
Everything else is just "technical details" I guess ... ;)
PS! - AMAZING question ...!! ;)
AJAX (Asynchronous JavaScript and XML) is a newly coined term for two powerful browser features that have been around for years, but were overlooked by many web developers until recently when applications such as Gmail, Google Suggest, and Google Maps hit the streets.
To know more information about Ajax learn Ajax tutorial
AJAX = Asynchronous JavaScript and XML.
AJAX is a technique for creating fast and dynamic web pages.
AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.
Classic web pages, (which do not use AJAX) must reload the entire page if the content should change.
Examples of applications using AJAX: Google Maps, Gmail, Youtube, and Facebook tabs.(FROM w3school). to understand simply: when we request for a link or submit form we request a synchronously to server for data. webpage destroy current page and regenerate new page. but with AJAX browser can send the same request without repainting the entire page.
It's JavaScript, but it works.
I recently came across http://chromeexperiments.com/. I found a couple of projects there that are quite intriguing: 100 Tweets and twitterbrowse (I'd post links to them but I'm not yet allowed). These both work fine for me in Firefox 3.5 under Ubuntu 9.04. The thing that I find particularly peculiar is the fact that these two "experiments" seem to issue Ajax requests to other domains than the ones they are hosted on (to twitter.com, more exactly). I have tried the same thing on an HTML5 page (using <!DOCTYPE html>), but I can't get it to work.
I'm using MooTools to create the requests, but that shouldn't be a problem, it's still Ajax, right?
Any idea how those sites are doing this?
XMLHttpRequest Level 2 allows for cross-domain AJAX. Read more about it here.
Have a look at http://snook.ca/archives/javascript/cross_domain_aj/
I personnaly was able to do this using the JSON method on a personal project where I had to receive ajax response from a different domain's server.
They aren't using HTML5 for the ajax request, they're using JSONP which is essentially a getter for JSON, but can be made across any domain